Planarization process, apparatus and method of manufacturing an article

ABSTRACT

A method is provided, comprising creating at least one crack at a point on an edge of a stack of at least a substrate and a superstrate; propagating the crack along the periphery; and moving the superstrate relative to the substrate to complete separation of the superstrate from the substrate.

BACKGROUND Field of Art

The present disclosure relates to substrate processing, and moreparticularly, to the planarization of surfaces in semiconductorfabrication.

Description of the Related Art

Planarization techniques are useful in fabricating semiconductordevices. For example, the process for creating a semiconductor deviceincludes repeatedly adding and removing material to and from asubstrate. This process can produce a layered substrate with anirregular height variation (i.e., topography), and as more layers areadded, the substrate height variation can increase. The height variationhas a negative impact on the ability to add further layers to thelayered substrate. Separately, semiconductor substrates (e.g., siliconwafers) themselves are not always perfectly flat and may include aninitial surface height variation (i.e., topography). One method ofaddressing this issue is to planarize the substrate between layeringsteps. Various lithographic patterning methods benefit from patterningon a planar surface. In ArFi laser-based lithography, planarizationimproves depth of focus (DOF), critical dimension (CD), and criticaldimension uniformity. In extreme ultraviolet lithography (EUV),planarization improves feature placement and DOF. In nanoimprintlithography (NIL) planarization improves feature filling and CD controlafter pattern transfer.

A planarization technique sometimes referred to as inkjet-based adaptiveplanarization (IAP) involves dispensing a variable drop pattern ofpolymerizable material between the substrate and a superstrate, wherethe drop pattern varies depending on the substrate topography. Asuperstrate is then brought into contact with the polymerizable materialafter which the material is polymerized on the substrate, and thesuperstrate removed. Improvements in planarization techniques, includingIAP techniques, are desired for improving, e.g., whole wafer processingand semiconductor device fabrication.

SUMMARY

A method is provided. The method comprises creating at least one crackat a point on an edge of a stack of at least a substrate and asuperstrate, propagating the crack along the periphery, and moving thesuperstrate relative to the substrate to complete separation of thesuperstrate from the substrate. The method may further compriseintroducing a positive fluid pressure between the substrate and thesuperstrate at the point on the edge to create the crack. The positivefluid pressure includes a flow of clean dry air, helium, or nitrogen.The method may further comprise retaining the superstrate in asuperstrate chuck with a negative fluid pressure and applying a highflow of negative fluid pressure to a peripheral zone on the superstrateto propagate the crack along the edge of the stack.

The positive fluid pressure is continuously introduced to the separatedportion while the high flow of negative fluid pressure is applied to theperipheral zone on the superstrate. The superstrate may be moved in adirection away from the substrate with a superstrate chuck. The methodmay further comprise applying a negative fluid pressure to a center zoneon the superstrate to complete the separation of the superstrate fromthe substrate with a superstrate chuck. The method may further compriseapplying a force at the point on an edge of the superstrate to createthe crack. Another crack may be created by applying a positive fluidpressure between the substrate and the superstrate at another point ofthe edge of the stack. The force may be applied by introducing apositive fluid pressure or a mechanical contact.

The method may further comprise stacking the substrate and thesuperstrate in such a way that the superstrate includes an overhangingedge portion; and applying a force to the overhanging edge portion tocreate a crack. Another edge portion of the superstrate may be alignedwith a notch at an edge portion of the substrate and a force is appliedto the another edge portion to create another crack between thesubstrate and the superstrate.

A chucking system is also provided. The system comprises a superstratechuck configured to retain a superstrate with negative fluid pressureand a source of force configured to apply a force to a point on an edgeof the superstrate stacked with a substrate, so as to create a crackbetween the substrate and the superstrate at the point on the edge. Thesuperstrate chuck includes a pattern of lands, and one of the landslocated near an edge of the superstrate chuck is recessed below theother lands located an inner portion of the superstrate chuck to allowthe superstrate to deflect towards the superstrate chuck while creatingthe crack. The chucking system may further comprise a substrate chuckconfigured to retain the substrate with negative fluid pressure. Thesubstrate chuck includes a pattern of lands, and one of the landslocated at an edge of the substrate chuck is recessed below the otherlands located at an inner portion of the substrate chuck to allow thesubstrate to deflect towards the substrate while creating the crack.

The source of force includes a mechanism to create a lateral mechanicalpush or a source of positive fluid pressure towards the edge of thesuperstrate. The substrate includes a notch arranged at an edge thereof,and the source of force includes a source of negative fluid pressureapplied to the superstrate via the notch. The chucking system mayfurther comprise a negative fluid pressure source to apply the negativefluid pressure to the superstrate through the superstrate chuck. Thesuperstrate chuck is configured to retain the superstrate such that thesuperstrate includes an overhanging portion. The source of force isconfigured to apply force to the overhanging portion of the superstrateto create the crack.

A method of manufacturing an article is provided. The method comprisesforming a cured material stacked between a substrate and a superstrate;creating at least one crack at a point at an edge between a substrateand a superstrate; propagating the crack along the periphery; andseparating the superstrate from the cured material.

These and other objects, features, and advantages of the presentdisclosure will become apparent upon reading the following detaileddescription of exemplary embodiments of the present disclosure, whentaken in conjunction with the appended drawings, and provided claims.

BRIEF DESCRIPTION OF DRAWINGS

So that features and advantages of the present invention can beunderstood in detail, a more particular description of embodiments ofthe invention may be had by reference to the embodiments illustrated inthe appended drawings. It is to be noted, however, that the appendeddrawings only illustrate typical embodiments of the invention and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

FIG. 1 is a diagram illustrating a planarization system;

FIGS. 2a to 2c illustrate a planarization process;

FIGS. 3a to 3b illustrate a multi-zone superstrate chuck in oneembodiment;

FIGS. 4a to 4e show the operation of the superstrate chuck for forming alayer on a substrate;

FIG. 5 is a flow chart of the planarization process as illustrated inFIGS. 4a to 4 e;

FIG. 6a shows a separation crack initiated at an edge of a stack of thesubstrate and the superstrate in one embodiment and FIG. 6b shows thealignment of a retractable pin with a substrate notch for initiationsuch separation crack;

FIG. 6c shows a separation crack initiated at an edge of a stack of thesubstrate and the superstrate in another embodiment;

FIGS. 7a to 7c show the top view of the stack of the substrate andsuperstrate as a separation crack is initiated and propagated about aperiphery of the stack;

FIG. 8 shows the separated substrate and superstrate;

FIG. 9 is a flow chart of the separation process as illustrated in FIGS.7 and 8;

FIG. 10 shows a separation crack initiated at an edge of a stack of thesubstrate and the superstrate in a further embodiment;

FIGS. 11a and 1 lb illustrate a multi-zone superstrate chuck in anotherembodiment with improved zone sealing; and

FIG. 12 shows an enlarged view of an exemplary trench structure within azone of the FIGS. 11a and 11b superstrate chuck.

Throughout the figures, the same reference numerals and characters,unless otherwise stated, are used to denote like features, elements,components or portions of the illustrated embodiments. Moreover, whilethe subject disclosure will now be described in detail with reference tothe figures, it is done so in connection with the illustrative exemplaryembodiments. It is intended that changes and modifications can be madeto the described exemplary embodiments without departing from the truescope and spirit of the subject disclosure as defined by the appendedclaims.

DETAILED DESCRIPTION Planarization System

FIG. 1 illustrates a system for planarization. The planarization system100 is used to planarize a film on a substrate 102. The substrate 102may be coupled to a substrate chuck 104. The substrate chuck 104 may bebut is not limited to a vacuum chuck, pin-type chuck, groove-type chuck,electrostatic chuck, electromagnetic chuck, and/or the like.

The substrate 102 and the substrate chuck 104 may be further supportedby a substrate positioning stage 106. The substrate positioning stage106 may provide translational and/or rotational motion along one or moreof the x-, y-, z-, θ-, ψ, and φp-axes. The substrate positioning stage106, the substrate 102, and the substrate chuck 104 may also bepositioned on a base (not shown). The substrate positioning stage may bea part of a positioning system.

Spaced apart from the substrate 102 is a superstrate 108 having aworking surface 112 facing substrate 102. Superstrate 108 may be formedfrom materials including, but not limited to, fused silica, quartz,silicon, organic polymers, siloxane polymers, borosilicate glass,fluorocarbon polymers, metal, hardened sapphire, and/or the like. In anembodiment the superstrate is readily transparent to UV light. Surface112 is generally of the same areal size or slightly smaller as thesurface of the substrate 108.

Superstrate 108 may be coupled to or retained by a superstrate chuck118. The superstrate chuck 118 may be, but is not limited to, vacuumchuck, pin-type chuck, groove-type chuck, electrostatic chuck,electromagnetic chuck, and/or other similar chuck types. The superstratechuck 118 may be configured to apply stress, pressure, and/or strain tosuperstrate 108 that varies across the superstrate 108. In an embodimentthe superstrate chuck is likewise readily transparent to UV light. Thesuperstrate chuck 118 may include a system such as a zone based vacuumchuck, an actuator array, a pressure bladder, etc., which can apply apressure differential to a back surface of the superstrate 108 to causethe template to bend and deform. In one embodiment, the superstratechuck 118 includes a zone based vacuum chuck which can apply a pressuredifferential to a back surface of the superstrate, causing thesuperstrate to bend and deform as further detailed herein.

The superstrate chuck 118 may be coupled to a planarization head 120which is a part of the positioning system. The planarization head 120may be movably coupled to a bridge. The planarization head 120 mayinclude one or more actuators such as voice coil motors, piezoelectricmotors, linear motor, nut and screw motor, etc., which are configured tomove the superstrate chuck 118 relative to the substrate 102 in at leastthe z-axis direction, and potentially other directions (e.g. x-, y-, θ-,ψ-, andφ-axis).

The planarization system 100 may further comprise a fluid dispenser 122.The fluid dispenser 122 may also be movably coupled to the bridge. In anembodiment, the fluid dispenser 122 and the planarization head 120 shareone or more of all positioning components. In an alternative embodiment,the fluid dispenser 122 and the planarization head move independentlyfrom each other. The fluid dispenser 122 may be used to deposit dropletsof liquid formable material 124 (e.g., a photocurable polymerizablematerial) onto the substrate 102 with the volume of deposited materialvarying over the area of the substrate 102 based on at least in partupon its topography profile. Different fluid dispensers 122 may usedifferent technologies to dispense formable material 124. When theformable material 124 is jettable, ink jet type dispensers may be usedto dispense the formable material. For example, thermal ink jetting,microelectromechanical systems (MEMS) based ink jetting, valve jet, andpiezoelectric ink jetting are common techniques for dispensing jettableliquids.

The planarization system 100 may further comprise a curing system thatincludes a radiation source 126 that directs actinic energy, forexample, UV radiation, along an exposure path 128. The planarizationhead 120 and the substrate positioning state 106 may be configured toposition the superstrate 108 and the substrate 102 in superimpositionwith the exposure path 128. The radiation source 126 sends the actinicenergy along the exposure path 128 after the superstrate 108 hascontacted the formable material 128. FIG. 1 illustrates the exposurepath 128 when the superstrate 108 is not in contact with the formablematerial 124. This is done for illustrative purposes so that therelative position of the individual components can be easily identified.An individual skilled in the art would understand that exposure path 128would not substantially change when the superstrate 108 is brought intocontact with the formable material 124.

The planarization system 100 may further comprise a camera 136positioned to view the spread of formable material 124 as thesuperstrate 108 contacts the formable material 124 during theplanarization process. FIG. 1 illustrates an optical axis 138 of thefield camera's imaging field. As illustrated in FIG. 1, theplanarization system 100 may include one or more optical components(dichroic mirrors, beam combiners, prisms, lenses, mirrors, etc.) whichcombine the actinic radiation with light to be detected by the camera136. The camera 136 may include one or more of a CCD, a sensor array, aline camera, and a photodetector which are configured to gather light ata wavelength that shows a contrast between regions underneath thesuperstrate 108 and in contact with the formable material 124 andregions underneath the superstrate 108 but not in contact with theformable material 124. The camera 136 may be configured to provideimages of the spread of formable material 124 underneath the superstrate108, and/or the separation of the superstrate 108 from cured formablematerial 124. The camera 136 may also be configured to measureinterference fringes, which change as the formable material 124 spreadsbetween the gap between the surface 112 and the substrate surface.

The planarization system 100 may be regulated, controlled, and/ordirected by one or more processors 140 (controller) in communicationwith one or more components and/or subsystems such as the substratechuck 104, the substrate positioning stage 106, the superstrate chuck118, the planarization head 120, the fluid dispenser 122, the radiationsource 126, and/or the camera 136. The processor 140 may operate basedon instructions in a computer readable program stored in anon-transitory computer memory 142. The processor 140 may be or includeone or more of a CPU, MPU, GPU, ASIC, FPGA, DSP, and a general-purposecomputer. The processor 140 may be a purpose-built controller or may bea general-purpose computing device that is adapted to be a controller.Examples of a non-transitory computer readable memory include but arenot limited to RAM, ROM, CD, DVD, Blu-Ray, hard drive, networkedattached storage (NAS), an intranet connected non-transitory computerreadable storage device, and an internet connected non-transitorycomputer readable storage device.

In operation, either the planarization head 120, the substrate positionstage 106, or both vary a distance between the superstrate 118 and thesubstrate 102 to define a desired space (a bounded physical extent inthree dimensions) that is filled with the formable material 124. Forexample, the planarization head 120 may be moved toward the substrateand apply a force to the superstrate 108 such that the superstratecontacts and spreads droplets of the formable material 124 as furtherdetailed herein. Planarization Process

The planarization process includes steps which are shown schematicallyin FIGS. 2a-2c . As illustrated in FIG. 2a , the formable material 124is dispensed in the form of droplets onto the substrate 102. Asdiscussed previously, the substrate surface has some topography whichmay be known based on previous processing operations or may be measuredusing a profilometer, AFM, SEM, or an optical surface profiler based onoptical interference effect like Zygo NewView 8200. The local volumedensity of the deposited formable material 124 is varied depending onthe substrate topography. The superstrate 108 is then positioned incontact with the formable material 124.

FIG. 2b illustrates a post-contact step after the superstrate 108 hasbeen brought into full contact with the formable material 124 but beforea polymerization process starts. As the superstrate 108 contacts theformable material 124, the droplets merge to form a formable materialfilm 144 that fills the space between the superstrate 108 and thesubstrate 102. Preferably, the filling process happens in a uniformmanner without any air or gas bubbles being trapped between thesuperstrate 108 and the substrate 102 in order to minimize non-filldefects. The polymerization process or curing of the formable material124 may be initiated with actinic radiation (e.g., UV radiation). Forexample, radiation source 126 of FIG. 1 can provide the actinicradiation causing formable material film 144 to cure, solidify, and/orcross-link, defining a cured planarized layer 146 on the substrate 102.Alternatively, curing of the formable material film 144 can also beinitiated by using heat, pressure, chemical reaction, other types ofradiation, or any combination of these. Once cured, planarized layer 146is formed, the superstrate 108 can be separated therefrom. FIG. 2cillustrates the cured planarized layer 146 on the substrate 102 afterseparation of the superstrate 108. The substrate and the cured layer maythen be subjected to additional known steps and processes for device(article) fabrication, including, for example, patterning, curing,oxidation, layer formation, deposition, doping, planarization, etching,formable material removal, dicing, bonding, and packaging, and the like.The substrate may be processed to produce a plurality of articles(devices). Spreading, Filling, and Curing Planarization Material BetweenSuperstrate and Substrate

One scheme for minimizing entrapment of air or gas bubbles between thesuperstrate 108 and the substrate as the formable material dropletsspread, merge and fill the gap between the superstrate and the substrateis to position the superstrate such that it makes initial contact withthe formable material in the center of the substrate with furthercontact then proceeding radially in a center to perimeter fashion. Thisrequires a deflection or bowing of the superstrate or substrate or bothto create a curvature profile in the superstrate. However, given thatthe superstrate 108 is typically of the same or similar areal dimensionas the substrate 102, a useful whole superstrate bowing curvatureprofile requires both a significant vertical deflection of thesuperstrate, and a concomitant vertical motion by the superstrate chuckand planarization assembly. Such a significant vertical deflection andmotion may be undesirable for control, accuracy, and system designconsiderations. Such a superstrate profile can be obtained by, forexample, applying a back pressure to the interior region of thesuperstrate. However, in doing so, a perimeter holding region is stillrequired to keep the superstrate retained on the superstrate chuck. Ifboth the perimeter edges of the superstrate and the substrate arechucked flat during formable material droplet spreading and merging,there will be no available superstrate curvature profile in this flatchucked area. This may compromise the droplet spreading and merging,which may also lead to non-fill defects in the region. In addition, oncespreading and filling of the formable material is complete, theresultant stack of a superstrate chuck, a chucked superstrate, theformable material, substrate, and a substrate chuck can be anover-constrained system. This may cause a non-uniform planarizationprofile of the resultant planarized film layer. That is, in such anover-constrained system, all flatness errors or variations from thesuperstrate chuck, including front-back surface flatness, can betransmitted to the superstrate and impact the uniformity of theplanarized film layer.

To resolve the above issues, in one embodiment, a multi-zone superstratechuck 118 is provided as shown in FIGS. 3a and 3b . The superstratechuck 118 includes a center zone 301 and a series of ring zones 303about the center zone 301. The ring zones 303 may be defined into aperipheral ring zone 303 b around an edge, a perimeter, or a peripheryof the superstrate chuck 118 and a plurality of inner ring zones 303 alocated between the center zone 301 and the peripheral ring zone 303 b.The multiple ring zones 303 may be defined by a series of lands 307protruding from a surface of the superstrate chuck 118. As shown inFIGS. 3a and 3b , the lands 307 may be formed about the center zone 301.In each of the ring zones 303, at least one port 305 is formed toconnect through the superstrate chuck 118, to allow a pressure source toapply positive pressure or negative pressure, for example, vacuum, to asuperstrate retained thereby.

FIG. 3b shows a side cross-sectional view of the superstrate chuck 118.Each of the lands 307 protrudes from a surface of the superstrate chuck118 with a height. The lands 307 include a peripheral land 307 bsurrounding the peripheral ring zone 303 b and a series of inner lands307 a between the center zone 301 and the peripheral ring zone 303 b. Asshown in FIG. 3b , the inner lands 307 a have substantially the sameheight, while the height of the peripheral land 307 b is less than thoseof the inner lands 307 a. The center zone 301 of the superstrate chuck118 may be in the form of a circular cavity, such that the pressuresource (not shown) may apply air or gas pressure through the associatedchannel 308 and port 305 to deflect a center portion of a retainedsuperstrate. Vacuum pressure may likewise be applied to center zone 301through the same channel and port. The center zone 301 of thesuperstrate chuck 118 may be aligned with a center portion of theretained superstrate. Similarly, the peripheral ring zone 303 a may bealigned with a perimeter or a periphery of the retained superstrate.Surrounding ring zones 303 are likewise provided with respectivechannels 308 and ports 305 for application of pressure or vacuum.

Turning to FIGS. 4a -4 e, a process for contacting, spreading andmerging droplets of deposited formable material 124 is depicted. Asshown in FIG. 4a , before the superstrate 108 is brought in contact withthe formable material 124, a positive pressure (indicated by arrow P) isapplied through ports 305 to the center zone 301 of the superstratechuck 118 to the retained superstrate 108 to deflect the center portionof the superstrate 108 towards the formable material 124. The pressure Pis applied to the center zone 301 to control an initial deflection at apredetermined range and to maintain a predetermined curvature of thesuperstrate 108 as shown in FIG. 4a . In the meantime, a negativepressure, preferably, a vacuum (indicated by arrows V), is applied tothe superstrate 108 through the ports 305 in the ring zones 303 toretain the superstrate 108 with the superstrate chuck 118. Thesuperstrate 108 is then brought into initial contact with the dropletsof formable material 124 as show in FIG. 4 b.

The deflection of the superstrate 108 is then extended from the centerportion in a radially outward direction by sequentially releasing thevacuum (V) from the inner ring zones 303 a proximal to the center zone301. In this fashion, the droplets of formable material are contacted,spread and merged to form a film layer with a fluid front thatprogresses radially outward as the superstrate contacts and conforms tothe substrate. When the vacuum is sequentially released from the innerring zones 303 a, the pressure P applied through the center zone 301 ismaintained at a desired value. Pressure P may also be applied to thesuperstrate 108 through the channels 308 and ports 305 in the inner ringzones 303 a from which the vacuum has been released. In the embodimentas shown in FIGS. 4c , vacuum has been sequentially released from threeinner rings 303 a closest to the inner zone 301, with pressure Psequentially applied as the vacuum has been sequentially released.Planarization head may also be moved downward during this sequentialvacuum release and pressurization.

The deflection of the superstrate 108 is then further extended in aradial direction sequentially until the vacuum is released from all theinner ring zones 303 a, while the vacuum V applied via the peripheralring zone 303 b is maintained. For each of the inner ring zones 303 a,pressure P is also applied once the vacuum has been released. As shownin FIG. 4d , when the vacuum has been released from all inner ring zones303 a, the superstrate 108 is deflected to conform to the substrate 102except for the periphery of substrate 108 which remains retained by thesuperstrate chuck 118 via the vacuum V applied through the peripheralzone 303 b. As such, the edge of superstrate 108 remains in a deflected,curved condition for the final spreading and merging of formablematerial droplets dispensed on the periphery of the substrate 102. Inaddition, the peripheral land 307 b, which is lower relative to theinner lands 307 a, facilitates the maintenance of such curvature.

In FIG. 4e , the vacuum V applied through the peripheral ring zone 303 bis then released to in order to release the superstrate 108 entirelyfrom the superstrate chuck 118. This provides multiple advantages.First, by releasing the periphery of superstrate 108 from the peripheralring zone 303 b which had been retained in a curved condition, thespreading and merging of the remaining formable material droplets can becompleted in the same center-to-perimeter radial fashion, thuscontinuing to minimize air or gas trapping and resultant non-filldefects. Specifically, the peripheral land 307 b which is recessedrelative to the inner lands 307 a allows the superstrate 108 to maintainthe desired curvature prior to release. Secondly, by completelyreleasing the superstrate 108 from the superstrate chuck 118, anyover-constraint of the superstrate 108 due to the chucking condition isremoved, thereby reducing local non-uniform planarization that mightotherwise occur due to such constrained conditions. Thirdly, the releaseof the superstrate 108 from the superstrate chuck 118 eliminates thetransfer of any chuck non-flatness error or variation to the superstrate108, which also reduces localized non-uniform planarization variations.

Once the superstrate 108 is released, curing energy may be applied tocure the formable material to form the planarized layer. As previouslymentioned, the curing source may a light beam for curing the formablematerial 124. In one embodiment, the size of the light beam may beadjusted or controlled with reference to a diameter of the superstrate.The light beam can also be controlled to be incident on the substratewith a predetermined angle. During curing, a lateral position (i.e., inX-Y plane) of the substrate 102 relative to a curing source may beadjusted. After the curing process, the superstrate 108 is re-retainedby the superstrate chuck 118 and superstrate 108 is then separated fromthe substrate as further described herein.

FIG. 5 illustrates a flow chart of the planarization process describedas shown in FIGS. 3 and 4. In Step 501, formable material droplets 124are dispensed on the substrate 102. The center zone of the superstrate108 is deflected towards the formable material droplets 124 in stepS502. The deflected superstrate 108 is then advanced by the superstratechuck 118 to be in contact with the formable material 124 in step S503.The deflection of the superstrate 108 is extended from the center zonetowards the perimeter of the superstrate 108 in step S504. Applicationof force to hold the superstrate 108 by the superstrate chuck 118, forexample, by vacuum applied to the perimeter of the superstrate 108 isthen stopped, such that the superstrate 108 is released (i.e.,de-chucked) from the superstrate chuck 118 in step S506. The formablematerial 124 is cured in step S507. After curing, the superstrate 108 isre-retained by the superstrate chuck 118 to separate the superstrate 108from the cured formable material 146.

When using, for example, a UV photocurable material as the formablematerial 124, it is desirable that the superstrate chuck 118 istransparent with high UV light transmissivity UV curing (as well as highlight transmissivity for imaging, for example, by the camera 136 asshown in FIG. 1). As discussed above, pneumatic supply channels 308 andports 305, zones 303, and lands 307 are integrated into the superstrateas shown in FIGS. 3 and 4. These structures may create a problem for UVcuring. Particularly, the UV transmissivity in areas below the channels308, and lands 307 can be significantly reduced compared to areas withno such features, leading to an under-curing or non-uniform curing ofthe formable material. This phenomenon is sometimes referred to as a“shadowing effect”. Shadowing effects may be particularly significant atedges of the lands 307. Additionally, when the superstrate 100 ischucked to the lands 307, there will be thin air gaps as two surfaces donot optically touch each other. This type of thin gap can sometimesblock UV completely. This phenomenon is known as the “thin film effect”between the land and the superstrate.

One solution to the above “shadow effect” includes movement of the stackof superstrate and substrate on a wafer stage in x, y and/or θcoordinates after de-chucking (i.e., releasing) the superstrate from thesuperstrate chuck. By moving the wafer stage in this fashion during UVexposure, regions of the superstrate and substrate that would haveremained under the channels, ports, and lands can be periodically movedto regions below the superstrate chuck where no chuck features arepresent. The relative motion required can be estimated from thefollowing equation (1):

$\begin{matrix}{{I_{m} = \frac{{I_{h}\left( {w_{h} - w_{l}} \right)} + {I_{l}w_{l}}}{w_{h}}},} & (1)\end{matrix}$

where I_(m) is the desired average intensity across range of motion,I_(h) is the high intensity across no feature area of the chuck (i.e.,the maximum or “max” intensity), I_(i) is the intensity at the subjectfeature (i.e., the lowest or “low” intensity), w_(h) is the estimatedmotion range to achieve I_(m), w_(l) is the subject feature width (e.g.,width of the land, port, or channel). For example, assuming 100% UVtransmission in the featureless areas, and assuming the desired I_(m) is90% of that value, and further assuming w_(i)=1 mm, from Equation (1),the desired range of relative motion w_(h)=8.0 mm. Alternatively, the UVsource can be moved by tipping or tilting the source relative to thesuperstrate chuck to change the angle of the UV light incident on thesuperstrate chuck, which can also reduce the shadowing effect near thesubject features. The “thin film effect” can be avoided by relativemovement in the z-axis direction to create a sufficient gap between thesuperstrate and superstrate chuck, for example, by de-chucking thesuperstrate and moving the wafer stage in the z-direction away from thesuperstrate chuck or. The various solutions described above can beapplied individually or in combination to improve the total UV dosageuniformity in certain regions and minimize shadowing and thin filmeffects. In various embodiments, the applied UV light beam can besmaller, same size, or larger than the substrate or superstrate. In oneembodiment, the applied UV light beam can be larger than the substrateby a dimension that accommodates the above relative motion w_(h) whilecontinuing to expose the entirety of the substrate to the UV light.Separating Superstrate from Cured Planarized Film Layer

Once the formable material is cured and the planarized film layer isformed, it is necessary to remove or release the superstrate from theformed layer. However, when the superstrate and substrate have the sameor similar areal dimensions, it is difficult to initiate and propagate aseparation crack between the superstrate and formed layer as isnecessary in order to fully separate the superstrate from the formedlayer. This problem can be resolved by the structure and methods shownin FIGS. 6-8. As shown in FIGS. 6a and 6b , substrate chuck 604 includesretractable pin 606 located at the periphery of the chuck that can bealigned with notch 608 on substrate 102. Such a notch (e.g. wafer notch)is common to semiconductor wafers for purposes of orienting the waferduring processing and handling. In operation, retractable pin 606 ispositioned in alignment with notch 608 located on substrate 102. Toinitiate separation, pin 606 moves upwardly through notch 608 and intocontact with a point 610 at the edge of superstrate 108, as shown inFIG. 6 a. The force applied by pin 606 is sufficient to initiateseparation crack 601 between superstrate 108 and cured layer 146 onsubstrate 102. Once the crack 601 is created, the edge of superstrate108 is deflected towards the superstrate chuck 118 by application ofvacuum pressure through port 305 of superstrate chuck 118. This isfacilitated by land 307 b of the superstrate chuck 118 being shorterthan the adjacent land 307 a, which provides a space for the edge ofsuperstrate 108 to be deflected away from the substrate 102 and towardsthe superstrate chuck 118. The force applied to create the crack 601 candepend upon the geometric and physical conditions of the superstrate,planarized film layer, and substrate. Alternatively, the crack 601 maybe created by introducing a positive pressure between the substrate 102and the superstrate 108, as shown in FIG. 6c . Here substrate chuck 614includes nozzle 616 connected to a positive fluid pressure source (notshown). Upon activation of nozzle 616, positive fluid pressure Pi isdelivered through nozzle 616 to point 610 at the edge of superstrate 118with sufficient force to initiate separation crack 601. The positivefluid pressure may include a flow of clean dry air, helium, or nitrogen.While creating the crack 601, the superstrate 102 is retained in thesuperstrate chuck 118, and the substrate 102 is retained by thesubstrate chuck 104.

FIGS. 7-8 illustrate the progression of separation. FIG. 7a shows a topdown view of the superstrate 118 in full contact (as indicated by theshaded region) with the formed layer on substrate. In FIG. 7b ,separation crack 601 has been initiated as described above. Once thecrack 601 is initiated, a high flow of negative pressure or vacuum isapplied to outer ring zone 303 b of superstrate chuck 118 so as toengage the edge of the superstrate 108 and propagate the separationcrack 601 about the outer zone ring 303 b. This propagation proceedscircumferentially in both directions from notch 608, as indicated byarrows C. To assist the propagation of crack 601 about the outer ringzone 303 b, additional lateral air flow (not shown) can be suppliedbetween the substrate 102 and the superstrate 108 as the crackpropagation progresses. FIG. 7c shows the crack 601 fully propagatedabout outer ring zone 303 b.

Once the separation crack has fully propagated around the outer ringzone, an upward motion may be applied along the Z-axis direction of thesuperstrate 108 to complete separation of the superstrate 108 from thecured layer on the substrate. FIG. 8 shows superstrate 108 fullyseparated from substrate 102. In completing separation, a significantupward motion of the superstrate 108 relative to the substrate 102 mayinduce a shearing stress at the remaining in-contact area between thesuperstrate 108 and the substrate 102. Alternatively, Z-direction motioncan be stopped at an earlier desired position and separation can beadvanced and concluded through continued vacuum pressure application tothe inner and/or center ring zones. Such shear stress can be minimizedby applying vacuum to one or more of the inner ring zones 303 a and/orthe center zone 301 during the continued separation.

FIG. 9 illustrates a flow chart of the separation process as describedand shown in FIGS. 7 and 8. In Step S901, a separation crack initiatedbetween the superstrate 108 and the cured layer. The separation crack isthen propagated about a periphery of superstrate 108 in step S902. Instep S903, the remainder of the superstrate is separated from the curedlayer. In the embodiments discussed above, the separation of thesuperstrate 108 and the substrate 102 includes a step of creating acrack by a mechanical force such as pushing pin or air pressure, a stepof applying vacuum pressure to the outer zone to propagate the crack,securely holding the superstrate 108, moving the superstrate 108upwardly in Z-direction and away from the substrate 102 with a forcesafe enough to avoid de-chucking the superstrate upwardly, and a step ofapplying vacuum to the center of the superstrate 108 during the upwardZ-direction movement to complete the separation. Alternatively or incombination with the above Z-direction motion schemes, the propagationof the separation can also be affected by continuously applying in-plane(or lateral) directional flow with high pressure from one or more sidesof the substrate (not shown).

In the FIG. 6 embodiments, crack initiation is initiated by an upwardforce applied through wafer notch 608 by either a mechanical pin 606(FIG. 6a ) or fluid nozzle 616 (FIG. 6b ). FIG. 10 shows a furtherembodiment of a substrate chuck configured to initiate a separationcrack. Here, substrate chuck 624 includes a separate retractable pin 626that can initiate a separation crack when the superstrate 108 andsubstrate are arranged non-concentrically. This non-concentricarrangement results in a portion 628 of the superstrate 108 thatoverhangs the substrate 102. The crack 602 can be created by applyingthe force to the overhanging portion 110 via movement of pin 626.Alternatively, the overhanging portion 608 may also be obtained by usinga superstrate slightly bigger than the substrate. In this way, thesuperstrate 108 can still be arranged concentric with the substrate 102.In either case, substrate chuck 624 can further include mechanical pinsor nozzles, such as in the embodiments of FIG. 6a or 6 b or otherwise,that are spaced apart from pin 626 to create multiple points about thesuperstrate periphery for initiating the separation crack.

Superstrate Chuck

As discussed above, the superstrate 108 is preferably retained orsupported by the superstrate chuck 118 that applies pressure or vacuum(negative pressure) to a volume between the superstrate and the chuckingsurface within ring zones 303 that are defined by lands 307 extendingfrom the chucking surface. Apart from the outermost land 307 a, theinner lands 307 b preferably have the same height such that the depthsof the gaps between the adjacent inner lands 307 b remains constant. Theland heights (i.e., depth of the gaps) is usually kept very small, forexample, in the order of about tens to thousands of microns, for reasonssuch as minimizing gas filling or evacuation response time, landstiffness characteristics, limiting thermal effects, such as expansionor contraction, etc. In operation, when vacuum is applied to a ring zoneto retain the superstrate against the lands of the zone, a vacuum sealis created at the superstrate-land interface. However, when a sufficientforce or a pressure is applied to the superstrate in the oppositiondirection of the chucking vacuum, the substrate may be lifted off theland of the chuck. At a certain gap between the superstrate and land,the vacuum seal fails or otherwise leaks resulting in a reduced or evenzero vacuum pressure within the zone. The superstrate may then becomeunintentionally de-chucked from the chuck. Further, even if superstrateis does not become de-chucked, vacuum leakage can disrupt the level ofcontrol required, for example, when sequentially releasing vacuumpressure in adjacent ring zones in the FIGS. 4 and 5 process. Suchleakage at the outer land can also negatively impact the controlledretention of the desired outer edge curvature of the superstrate in theprocess of FIGS. 4 to 5. Similarly, outer land leakage can disrupt theseparation crack initiation and propagation in the process of FIGS. 7 to9.

To counter such undesirable leakage, superstrate chuck 1118 is providedthat incorporates trench structures 1109, as shown in FIGS. 11a and 11b. Similar to superstrate chuck 118, the superstrate chuck 1118 likewiseincludes a plurality of lands 307, which can be defined into a series ofinner lands 307 a and a peripheral land 307 b protruding from a surface1119 of the superstrate chuck 1118. As shown in FIGS. 11b and 12, thesurface 1119 is the holding or retaining surface for holding orretaining the superstrate 108. A series of inner zones 303 a are definedby the lands 307 a. In at least one of the ring zones 303, a trench 1109is formed that is recessed from the surface of the chuck 1118. Thetrench can be concentric and positioned between the corresponding landsof the ring zone. Trenches 1109 a formed in the inner ring zones 303 aare positioned at locations distal to the center of the chuck 1118 withrespect to the associated inner ring zone width. In contrast, the trench1109 b formed in the peripheral ring zone 303 b is positioned at an areaproximal to the center of the substrate chuck 1118 relative to the outerzone ring width. That is, the trenches 1109 a formed in the inner ringzones 303 a are formed at an outer diameter of the corresponding innerring zones 303 a, while the trench 1109 b formed in the peripheral ringzone 303 b is formed at an inner diameter of the peripheral zone 303 b.

In operation, trenches 1109 act as a buffer that provides a uniformsource of high vacuum pressure that continues to act on the superstrateeven in the presence of a gap between superstrate at the land distal tothe trench. In this fashion, the sequential outwardly radial release ofvacuum and application of positive pressure to the center zone andadjacent ring zones can proceed in a controlled manner. That is, theapplied vacuum pressure in a given ring zone can be maintained, even aspositive pressure is applied to the adjacent inner zone in an amountthat may deflect the superstrate enough to produce a gap at the distalland. In other words, the provision of trenches 1109 allow for someleakage to be tolerated, without disruption to the intended process.Similarly, the trench 1109 b located in the peripheral ring zone withsmaller outer land height operates to maintain adequate vacuum pressurein the outer ring zone even in the presence of a small gap at the outerland. This enables the outer periphery of the superstrate to be held atthe desired curvature both for final spreading and merging of depositedformable material droplets (see FIG. 4d ) and for separation crackinitiation and propagation (see e.g. FIG. 6), even in the presence ofsome leakage.

FIG. 12 is an enlarged cross-sectional view of exemplary trenchstructure 1109 b. The particular trench dimensions and relevant locationwithin the ring zone needed to achieve the desired vacuum bufferingperformance is dependent upon the superstrate chuck land heights andring zone width. In the example shown in FIG. 12, the trench 1109 b islocated within ring zone 303 b and recessed from the chuck surface. Inthis example, the outer land 307 b has a height hi less than a height h₂of the inner land 307 a. In typical usage, the differences in landheights may range from about 5 microns to about 50 microns. Ring zone303 b has a width d. Trench 1109 b is positioned with a first edge at adistance d₁ from land 307 b and a second edge at a distance d₂ from land307 a. Trench 1109 b has a depth h₃ and a width d₃. In this embodiment,the relationship between these parameters satisfies the followingconditions:

h₁<h₂

h₃>10h₂

d₃<0.5 d

d ₁ >d ₂ +d ₃.

The port 305 connecting the trench 1109 b to the pressure supply (notshown) intersects with or is otherwise located within the trench. If theport does not intersect with the trench, the requisite high pressurecannot be maintained, and the trench will be ineffective. In the aboveembodiment, the outer land h₁ is where the leakage is expected to occur.For inner ring trenches 1109 b, the land heights may be the same, i.e.,h₁=h2. In this case, the distance d₁ is measured from the designatedland (i.e., h₁ or h₂) where the leakage is expected. For example, in theembodiment of FIGS. 11a and 11 b, the inner rings zone 303 a includetrenches 1109 a positioned closer to the outer lands (as measuredradially from the chuck center) of their respective ring zones tomitigate against leakage at the inner lands during the sequential vacuumrelease and subsequent pressurization of the ring zones as described inthe processes associated with FIGS. 4-5.

Further modifications and alternative embodiments of various aspectswill be apparent to those skilled in the art in view of thisdescription. Accordingly, this description is to be construed asillustrative only. It is to be understood that the forms shown anddescribed herein are to be taken as examples of embodiments. Elementsand materials may be substituted for those illustrated and describedherein, parts and processes may be reversed, and certain features may beutilized independently, all as would be apparent to one skilled in theart after having the benefit of this description.

1. A method, comprising: creating at least one crack at a point on anedge of a stack of at least a substrate and a superstrate for initiatingseparation between the substrate and the superstrate; propagating thecrack along the periphery; and moving the superstrate relative to thesubstrate to complete separation of the superstrate from the substrate.2. The method of claim 1, further comprising introducing a positivefluid pressure between the substrate and the superstrate at the point onthe edge to create the crack.
 3. The method of claim 2, wherein thepositive fluid pressure includes a flow of clean dry air, helium, ornitrogen.
 4. The method of claim 1, further comprising: retaining thesuperstrate in a superstrate chuck with a negative fluid pressure; andapplying a high flow of negative fluid pressure to a peripheral zone onthe superstrate to propagate the crack along the edge of the stack. 5.The method of claim 4, further comprising continuing to introduce thepositive fluid pressure to the separated portion while applying the highflow of negative fluid pressure to the peripheral zone on thesuperstrate.
 6. The method of claim 1, further comprising moving thesuperstrate in a direction away from the substrate with a superstratechuck.
 7. The method of claim 1, further comprising applying a negativefluid pressure to a center zone on the superstrate to complete theseparation of the superstrate from the substrate with a superstratechuck.
 8. The method of claim 1, further comprising applying a force atthe point on an edge of the superstrate to create the crack.
 9. Themethod of claim 8, further comprising creating another crack by applyinga positive fluid pressure between the substrate and the superstrate atanother point of the edge of the stack.
 10. The method of claim 1,wherein the force is applied by introducing a positive fluid pressure ora mechanical contact.
 11. The method of claim 1, further comprising:stacking the substrate and the superstrate in such a way that thesuperstrate includes an overhanging edge portion; and applying a forceto the overhanging edge portion to create a crack.
 12. The method ofclaim 11, further comprising: aligning another edge portion of thesuperstrate with a notch at an edge portion of the substrate andapplying a force to the another edge portion to create another crackbetween the substrate and the superstrate.
 13. A chucking system,comprising: a superstrate chuck configured to retain a superstrate withnegative fluid pressure; and a source of force configured to apply aforce to a point on an edge of the superstrate stacked with a substrate,so as to create a crack between the substrate and the superstrate at thepoint on the edge for initiating separation between the substrate andthe superstrate.
 14. The chucking system of claim 13, wherein thesuperstrate chuck includes a pattern of lands, and one of the landslocated near an edge of the superstrate chuck is recessed below theother lands located an inner portion of the superstrate chuck to allowthe superstrate to deflect towards the superstrate chuck while creatingthe crack.
 15. The chucking system of claim 13, further comprising asubstrate chuck configured to retain the substrate with negative fluidpressure.
 16. The chucking system of claim 15, wherein the substratechuck includes a pattern of lands, and one of the lands located at anedge of the substrate chuck is recessed below the other lands located atan inner portion of the substrate chuck to allow the substrate todeflect towards the substrate while creating the crack.
 17. The chuckingsystem of claim 13, wherein the source of force includes a mechanism tocreate a lateral mechanical push or a source of positive fluid pressuretowards the edge of the superstrate.
 18. The chucking system of claim13, wherein the substrate includes a notch arranged at an edge thereof,and the source of force includes a source of negative fluid pressureapplied to the superstrate via the notch.
 19. The chucking system ofclaim 13, further comprising a negative fluid pressure source to applythe negative fluid pressure to the superstrate through the superstratechuck.
 20. The chucking system of claim 13, wherein the superstratechuck is configured to retain the superstrate such that the superstrateincludes an overhanging portion; and the source of force is configuredto apply force to the overhanging portion of the superstrate to createthe crack.
 21. A method of manufacturing an article, comprising: forminga cured material stacked between a substrate and a superstrate; creatingat least one crack at a point at an edge between a substrate and asuperstrate for initiating separation between the substrate and thesuperstrate; propagating the crack along the periphery; and separatingthe superstrate from the cured material.
 22. The method of claim 1,further comprising pushing the superstrate towards a direction away fromthe substrate at the point at the edge to create the separation crack.